Indonesian state oil and gas producer PT Pertamina will acquire a 15% in the Mahakam gas block from France's Total SA (TOT) this year, possibly via an asset swap in which Total would gain a stake in one of Pertamina's concessions, the Indonesian firm's chief executive said Monday.

Total agrees to the deal but has asked Pertamina to exchange a stake in one of its own blocks, CEO Karen Agustiawan told reporters.

"We understand this, as no oil company wants to lose (part of) its portfolio," Agustiawan added. Her comments came following a trip to Paris last week when officials from Pertamina and Total met to discuss Pertamina's plan to buy part of Mahakam, which is located in eastern Indonesia and is one of the Southeast Asian nation's largest gas deposits.

Agustiawan said Pertamina has yet to decide which asset might be exchanged for the Mahakam stake. She gave no further details on the possible timing of the purchase.

An official at Total's France headquarters declined to comment on the matter.

Total and Japan's Inpex Corp. (1605.TO) each own a 50% stake in the Mahakam block. Total operates the block through its local unit Total E&P Indonesie.

Pertamina had earlier said it hopes to buy a 15% initial stake in Mahakam and then increase its holding in the block to 50% by 2017, when Total's current operating contract expires.

Total is in negotiations with the Indonesian government to extend its contract to operate Mahakam beyond the 2017 deadline, but it is unclear whether the extension will be approved.

The government has hinted that it will grant the extension, but in return may pressure Total to farm out a stake in the block to a local party, most likely Pertamina.

Philippe Armand, the then-head of Total E&P Indonesie, said last year that the company would welcome participation by a local partner.

Total estimates Mahakam contains 11 trillion cubic feet of gas reserves - enough to continue production at the block for 25 years.

-By Deden Sudrajat, contributing to Dow Jones Newswires; 62 21 3983 1277; Reuben.Carder@dowjones.com